The present invention relates to a process for the preparation of granular detergent or cleaning compositions with a wide range of bulk densities of between about 300-1300 g/l. More particularly the process of the invention makes use of a novel combination of high or low speed mixer/granulator in combination with a very low shear granulator. There has been considerable interest in detergent industry to develop processes for the production of granulated detergent powders exhibiting specific bulk densities. In the detergent industry powders exhibiting different bulk densities are available and specific processes are used to target specific ranges of bulk densities.
There are a number of single step processes which produce powders within a very narrow range of bulk densities. Two stage granulation processes for production of powders of bulk densities greater than 600 g/l are also known.
JP 60 072 999A (Kao) and GB 2 166 452B (Kao) disclose processes in which detergent sulphonic acid, sodium carbonate and water are mixed in a strongly shearing apparatus; the solid mass obtained is cooled to 40.degree. C. or below and pulverized; and the fine powder thus obtained is granulated.
There has also been considerable recent interest in the use of high-speed mixer/granulators in the preparation of high-bulk-density detergent powders. For example, EP 158 419B (Hashimura) discloses a process in which nonionic surfactant and soda ash are mixed and granulated in a reactor having horizontal and vertical blades rotating at different speeds, to give a detergent powder built with sodium carbonate and containing a high level of nonionic surfactant. Patent Application No. WO93/23523 describes a process for the continuous production of granular detergent and/or cleaning compositions exhibiting bulk densities between 600 and 1100 g/l by a two-stage granulation in two mixer/granulators arranged in series where 40-100% of the solid and liquid ingredients based on the total weight of solid and liquid ingredients used is pregranulated in a first low speed mixer granulator and the granulate from the first stage is mixed with the remaining solid and/or liquid ingredients in a second high speed mixer granulator and converted into a granulate where the content of the granules having diameters greater than 2 mm is less that 25 wt. per cent. The low speed granulator used in the first granulation stage provided peripheral velocities of the mixing elements between 2 m/s and 7 m/s. Preferred low speed mixer granulators are, e.g., the plough mixers made by Lodige, Germany and the intensive mixer made by IMAPVC, Germany. The high speed mixer granulator provides for a peripheral velocity of the mixing elements of 8 m/s to 35 m/s. A suitable high speed mixer granulator is, for example, that made by Schugi, The Netherlands.
Indian Patent No. 170497 describes a process for preparing a high bulk density granular detergent composition with bulk density of at least 650 g/l which comprises treating a particulate starting material in a first step in a high speed mixer/densifier, the mean residence time being about 5-30 seconds and in a second step in a moderate-speed granulator/densifier whereby it is brought into or maintained in a deformable stage, the mean residence time being 1-10 minutes, and a final step in a drying and/or cooling apparatus. Preferably, the particle starting material is already brought into and/or maintained in a deformable stage in the first step. An example of a suitable high speed mixer/densifier which may be used in this process is Lodige CB30 recycler. Other examples of suitable high speed mixers/densifiers are, for instance, Schugi.RTM. granulator or a Draise.RTM. K-TTP80. An example of a suitable moderate speed granulator/densifier which may be used in this process is a Lodige.RTM. KM300 mixer also referred to as a plough share mixer. Another suitable machine is, for example, Draise.RTM. K-T160.
Our copending application no. 92203563.9 (EP 544,365) describes a detergent composition and a continuous process of producing detergent powders having bulk density of, for example, 600 g/l and above. This invention comprises treating a particulate starting material in a high speed mixer/densifier characterised in that 0.1-50% by weight as calculated on the granular detergent surfactant of liquid surfactant composition is mixed with the starting material during the treating process. For obtaining a very high bulk density powder, the detergent powder obtained by the process of the invention may be further treated in a second step in a moderate speed granulator/densifier whereby it is brought into or maintained in a deformable state, the mean residence time being 1-10 minutes and thereafter in a third step in drying/cooling apparatus for example as described in EP-A-367, 339.
Thus, high bulk density powders have either been produced by a single step granulation or by a suitable combination of a low speed mixer granulator in combination with a high speed mixer granulator or a high speed mixer granulator combined with a low speed mixer granulator. The low speed mixer granulators generally operate with tip speeds in the range 2-7 m/s and the high speed granulators operate with tip speeds in the range 8-35 m/s.
It is an object of the present invention to provide a process for preparing granular detergent or cleaning compositions in which the bulk density of the compositions may be selected as desired between 300-1300 g/l.